GRILLES COVERING SWIMMING POOL OUTLETS
Further guidance from PWTAG and ISRM

In October 2001, a notice under this heading from the Health and Safety Executive (HSE), which has been circulated to some pool operators, mentioned two figures for the maximum size holes or gaps in sump drain grilles.

A maximum of 8mm was quoted as the current industry guidance. The notice then went on to say that, where risk assessment indicated a significant risk of entrapment, a change to a 4mm figure might need to be considered. Subsequent reports and deliberations suggest that this advice requires some clarification and amendment.

Neither the Pool Water Treatment Advisory Group (PWTAG) nor the Institute of Sport & Recreation Management (ISRM) would encourage pool operators to change from 8mm to 4mm gaps, unless for some reason total exclusion is found by risk assessment to be necessary. But with no evidence of any accidents from entrapment in8mm grilles this is highly unlikely. More important, if 4mm gaps were to be used, operators would also have to ensure that the size or number of the outlets were increased to ensure that the water flow through the grille was less than 0.5m/sec. Also, frquent inspections and maintenance of the grilles would be imperative to avoid partial clogging, build up in velocity and the consequent dangers.

In terms of the risk of injury through toes or fingers becoming entrapped in an outlet, there have never been any recorded cases of this with grilles using 8mm gaps. On the contarary 8mm is the figure universally adopted for equipment used by children throughout Europe, America, Australia and New Zealand. 8mm is also the figure given in the HSE publication, Managing Health and Safety in Swimming Pools, and that used in the CEN safety standard for the construction of swimming pool equipment.

If 4mm gaps were simply used to replace 8mm gaps, this would increase suction through the grille, creating an even greater danger of entrapment. Further, using 4mm gaps would in effect turn the grille into a strainer for small objects like plasters, leaves; these are likely to accumulate on top of the grille, further restricting flow and increasing suction velocities. The result could be very dangerous and costly if the flow becomes blocked.

The 4mm figure was based on the standards used for guards to protect people from moving machinery where total exclusion is required to prevent contact with moving parts. These circumstances do not apply to a swimming pool outlet.

So the current guidance is as stated in PWTAG's book, Swimming Pool Water, in ISRM's guidance notes and in HSE's book, Managing Health & Safety in Swimming Pools. Gaps in sump drain grilles should not exceed 8mm maximum.

This guidance note has been prepared in consultation with the Health & Safety Executive.

SWIMMING POOL WATER Treatment & Quality Standards (ISBN 0 9517007 66) is £35 (UK), £45 (Overseas) including post and packing. It is 144 pages and distributed by Greenhouse Publishing (tel: +44 (0)1379 890721 or fax: +44 (0)1379 898244). Bulk supplies (in boxes of 33) are available from PWTAG's secretary.